1. Field of the Invention
This invention relates to the field of suspensions for hard disk drives. More particularly, this invention relates to methods of assembling suspensions using microactuators having partially cured adhesives, and methods of producing microactuator motors having wrap-around electrodes.
2. Description of Related Art
Magnetic hard disk drives and other types of spinning media drives such as optical disk drives are well known. FIG. 1 is an oblique view of an exemplary prior art hard disk drive and suspension for which the present invention is applicable. The prior art disk drive unit 100 includes a spinning magnetic disk 101 containing a pattern of magnetic ones and zeroes on it that constitutes the data stored on the disk drive. The magnetic disk is driven by a drive motor (not shown). Disk drive unit 100 further includes a disk drive suspension 105 to which a magnetic head slider (not shown) is mounted proximate a distal end of load beam 107. Suspension 105 is coupled to an actuator arm 103, which in turn is coupled to a voice coil motor 112 that moves the suspension 105 arcuately in order to position the head slider over the correct data track on data disk 101. The head slider is carried on a gimbal which allows the slider to pitch and roll so that it follows the proper data track on the disk, allowing for such variations as vibrations of the disk, inertial events such as bumping, and irregularities in the disk's surface.
Both single stage actuated disk drive suspensions and dual stage actuated (DSA) suspension are known. In a single stage actuated suspension, only voice coil motor 112 moves suspension 105.
In a DSA suspension, as for example in U.S. Pat. No. 7,459,835 issued to Mei et al. as well as many others, in addition to voice coil motor 112 which moves the entire suspension, at least one microactuator is located on the suspension in order to effect fine movements of the magnetic head slider to keep it properly aligned over the data track on the spinning disk. The microactuator(s) provide much finer control and much higher bandwidth of the servo control loop than does the voice coil motor alone, which effects relatively coarse movements of the suspension and hence the magnetic head slider. A piezoelectric element or component, made of piezoelectric material, sometimes referred to simply as a PZT, is often used as the microactuator motor, although other types of microactuator motors are possible. In the discussion that follows, for simplicity the microactuator will be referred to simply as a “PZT,” although it will be understood that the microactuator need not be of the PZT type.
FIG. 2 is a top plan view of the prior art suspension 105 in FIG. 1. Two PZT microactuators 14 are affixed to suspension 105 on microactuator mounting shelves 18 that are formed within base plate 12, such that the PZTs span respective gaps in base plate 12. Microactuators 14 are affixed to mounting shelves 18 by non-conductive epoxy 16 at each end of the microactuators. The positive and negative electrical connections can be made from the PZTs to the suspension's flexible wiring trace and/or to the grounded base plate by a variety of techniques including those disclosed in commonly owned U.S. Pat. No. 7,751,153 to Kulangara et al.
In assembling a DSA suspension, the process typically includes the steps of: dispensing liquid adhesive such as epoxy onto the suspension and/or the PZT; positioning the PZT into place on the suspension; and curing the adhesive, typically by thermal curing, ultraviolet (“UV”) curing, or other curing methods depending on the adhesive used. DSA suspensions often include both conductive epoxies and/or non-conductive epoxies to bond the PZT to the suspension. Conductive adhesives, such as silver-containing epoxies, are well known and are commonly used.
FIG. 3 shows a prior technique for bonding two PZTs in a DSA suspension including the electrical connection therebetween. FIG. 3 is not admitted as being “prior art” within the legal meaning of that term. Similarly, the processes described herein as applicable to FIG. 3 are also not admitted as being “prior art” within the legal meaning of that term. FIGS. 4 and 5 are cross sectional views taken along section lines C-C′ and D-D′ in FIG. 3, respectively, showing the details of the bonding. As best seen in FIG. 4, the PZT 330 has electrodes on both sides where the bottom electrode is grounded at one end by conductive epoxy 324 through gold 326 on grounded stainless steel 328 layer, and insulated at the other end by non-conductive epoxy 320. As best seen in FIG. 5, the top electrode is connected to a copper electrical contact pad 316 which is part of the suspension's electrical interconnect or flexible circuit and is insulated from the stainless steel substrate 312 by insulating layer 314 such as polyimide, by conductive epoxy 322 over non-conductive epoxy 320. Electrical contact pad 316 provides the driving voltage for PZT 330. Non-conductive epoxy 320 is primarily responsible for the mechanical bond between PZT 330 and stainless steel substrate 312. In general, the height of the conductive epoxy 322 for the top electrode is difficult to control, and the overall PZT attachment process requires three epoxy bonding steps, which is time consuming and costly. Also, two separate curing steps are required for the epoxy on the bottom electrode and on the top electrode.
There are drawbacks to the prior methods of bonding PZTs to suspensions. It can be difficult to control exactly how much epoxy is dispensed, where the adhesive ends up due to flow of the liquid adhesive, and other issues. Various solutions have been proposed that involve, for example, channels underneath the PZTs to control the flow of adhesive and to channel any excess liquid epoxy away from sensitive areas. U.S. Pat. No. 6,856,075 to Houk, for example, proposes an adhesive attachment that has one or more reliefs under or partially under or adjacent to a PZT transducer to control the flow of adhesive by limiting or influencing adhesive travel or flow and simultaneously preventing excessive adhesive fillet height adjacent the piezoelectric motor. Additionally, if the PZT is located at or near the gimbal which carries the magnetoresistive read/write head, it becomes critical to be able to predict and control the flow of adhesive because differences in adhesive flow and distribution from one part to another can adversely affect the geometries, mechanical properties, and resulting performance of the suspension. These issues are particularly pronounced when the PZT is located at a particularly sensitive part of the suspension such as near or at the gimbaled head slider. Repeatability and predictability are especially critical in that area. Still further, the presence of liquid epoxy and its dispensing equipment within the final assembly room represents both a potential source of contamination, as well as an additional and expensive manufacturing step.
Another drawback to the prior attachment means is the delays in assembly time required for multiple rounds of epoxy, including both conductive epoxy and non-conductive epoxy, to be dispensed and then cured. FIG. 6. illustrates the typical manufacturing process for PZT attachment, in which liquid epoxy is applied to the PZT, the interconnect, and/or the load beam before attaching the PZT. Conductive epoxy is dispensed at the interconnect (610), then non-conductive epoxy is dispensed at the load beam or other location for the PZT (612). The PZT is attached to the suspension (614), and the epoxy is then cured (616) in a first curing step. Next, conductive epoxy is dispensed again (618), and then cured (620) in a second curing step.